Appendix F

Appendix F                              Periodic Tests


Power Up Test


The power up test consists of simply opening the plastic lid of the MiniRes and pushing the "POWER" switch.  No wires should be attached to the binding posts for this test.  The MiniRes should power up for 30 to 50 seconds after pushing the "POWER" switch, then the instrument will automatically turn off unless the switch is pushed again during the interval.


At the instant that the "POWER" switch is activated, the "BATTERY LOW" LED should also turn on for a fraction of a second.  This confirms that the battery voltage sensing and indicator circuitry is operating properly.  Failure of this LED to light suggests a problem with the battery voltage sensing and indicator circuitry. A continually lit LED suggests weak batteries.


The "LINE OPEN" LED should illuminate and stay lit until the MiniRes automatically shuts off.  This LED is correctly indicating that the transmitter lines are not properly hooked up. 


The DPM (4.5 digit Digital Panel Meter) should come on and settle to a reading close to zero within a few seconds.  This specific reading of the DPM is called the "open circuit zero reading".  The "open circuit" refers to the receiver circuit input being "open" (no wires attached to it).  The actual reading of the instrument will significantly deviate from zero if any of the binding posts have even the slightest amount of moisture or dirt on (or in) them.  Keep these posts clean and dry for the best measurements! A PERFECTLY clean and dry MiniRes will have an "open circuit zero reading" of between -0010 and +0010.  A seriously dirty unit will have a reading less than -1000 or greater than +1000.



Shorted Input Test


This test is identical to the "POWER UP TEST" with the exception that the input (receiver) red and black binding posts (P+ and P-) are shorted together with a short wire (an unraveled paper clip is ideal for this test).  The transmitter binding posts (C+ and C-) are left unconnected.



The purpose of the "shorted inputs" test is to assure that the instrument can generate an accurate zero measurement.  A perfectly operating MiniRes should settle to display +1, 0 or -1 on the DPM (Digital Panel Meter) during this test, although from -3 to +3 is within specifications.  Any reading that has settled to a value outside this range is reason for concern.  The prime suspect is probably moisture or dirt on or between the binding posts.  Note that this specification holds for both the LOW “RANGE” (199.99 Ohm) and the HIGH “RANGE” (19.999 Ohm).


Accuracy Or Calibration Test


This test is the most thorough test of the entire instrument.  It checks the transmitter and receiver circuits. The test can be performed with the calibration harness supplied with the MiniRes or with an easily obtained resistor and some wire. If the LRI calibration harness is not available, a precision resistor of 1000.0 to 1900.0 ohms is required. The resistor should have an accuracy of, at least, 0.1% and, ideally, 0.01%.  Also, two short wires that can reach between the transmitter and receiver binding posts are required for this test. 


Connect the calibration harness according to the color-coding. If the LRI calibration harness is not available, connect the resistor between C+ and C-, then attach one of the wires between C+ and P+ and the other wire between C- and P-.  Tighten the binding posts lightly with your fingers.  No other wires should be connected to the binding posts. 


Switch the "RANGE" switch to HIGH (19.999 Ohms).  Now, power up the MiniRes.  After a few seconds, the DPM reading should settle to the accuracy specifications for the MiniRes.   For example, on the 19.999 Ohm range, a true 1500 ohm resistor should read a maximum of 1508 ohms and a minimum of 1492 ohms.  Now switch the "RANGE" switch to LOW (199.99 Ohms).  A true 150.0 ohm resistor should read a maximum of 150.35 and a minimum of 149.65 ohms.                                                           

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